System and method for programmably controlling electrode activation sequence in a multi-site cardiac stimulation device

ABSTRACT

An implant able multi-chamber cardiac stimulation device includes flexibly programmable electrode sensing configurations, and is capable of precisely controlling the stimulation sequence between multiple sites. The stimulation device provides a plurality of connection ports that allow independent connection of each electrical lead associated with a particular stimulation site in the heart. Each connection port further provides a unique terminal for making electrical contact with only one electrode such that no two electrodes are required to be electrically coupled. Furthermore, each electrode, whether residing on a unipolar, bipolar or multipolar lead, may be selectively connected or disconnected through programmable switching circuitry that determines the electrode configurations to be used for sensing and for stimulating at each stimulation site. The stimulation device possesses unique sensing and output configurations associated with each stimulation site, such that depolarizations occurring at each stimulation site can be detected independently of events occurring at other sites within the heart, and such that each site can be stimulated independently of other sites or on a precisely timed basis triggered by events occurring at other sites. The stimulation device is further capable of uniquely programming coupling intervals for precisely controlling the activation sequence of stimulated sites. Coupling intervals are selected so as to provide optimal hemodynamic benefit to the patient.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of copending U.S. application Ser. No.09/835,006, filed Apr. 12, 2001, titled “System and Method forAutomatically Selecting Electrode Polarity During Sensing andStimulation.”

FIELD OF THE INVENTION

This invention relates generally to programmable cardiac stimulatingdevices. More specifically, the present invention is directed to animplant able stimulation device and associated method for controllingthe electrode sensing and stimulation configurations and the activationsequence in a multi-chamber cardiac stimulation device using noninvasiveprogramming techniques.

BACKGROUND OF THE INVENTION

In a normal human heart, the sinus node, generally located near thejunction of the superior vena cava and the right atrium, constitutes theprimary natural pacemaker initiating rhythmic electrical excitation ofthe heart chambers. The cardiac impulse arising from the sinus node istransmitted to the two atrial chambers, causing a depolarization knownas a P-wave and the resulting atrial chamber contractions. Theexcitation pulse is further transmitted to and through the ventriclesvia the atrioventricular (A-V) node and a ventricular conduction systemcausing a depolarization known as an R-wave and the resultingventricular chamber contractions.

Disruption of this natural pacemaking and conduction system as a resultof aging or disease can be successfully treated by artificial cardiacpacing using implant able cardiac stimulation devices, includingpacemakers and implant able defibrillators, which deliver rhythmicelectrical pulses or other anti-arrhythmia therapies to the heart at adesired energy and rate. One or more heart chambers may be electricallystimulated depending on the location and severity of the conductiondisorder.

Cardiac pacemakers conventionally stimulate a heart chamber by applyingcurrent pulses to cardiac tissues via two electrodes, a cathode and ananode. Standard pacing leads are available in either of twoconfigurations, unipolar leads or bipolar leads, depending on thearrangement of the electrodes of a particular lead. A unipolar pacinglead contains a single electrode, normally the cathode, which extendspervenously distal from the pacemaker in an insulating enclosure untilit is adjacent to the tip of the lead where the insulation is terminatedto provide for electrical contact of the cathode with the heart tissue.The anode provides a return path for the pacing electrical circuit. Fora unipolar lead, the anode is the pacemaker case.

A bipolar lead contains two electrodes within an insulating sheath, ananode that extends distal from the pacemaker to a position adjacent to,but spaced from, the electrode tip, and a cathode that also extendsdistal from the pacemaker, but terminates a short distance distal of theanode, at the lead tip. The anode commonly takes the form of a ringhaving greater surface area than the cathode tip. An insulating barrierseparates the cathode and anode of a bipolar lead. In present-daypacemakers, circuits for pacing and sensing, which determine tip, ringand case electrode connections, are provided. Thus, the pacemakers canbe programmed via telemetry for either bipolar or unipolar operationwith respect to either sensing or pacing operations.

A single-chamber pacemaker delivers pacing pulses to one chamber of theheart, either one atrium or one ventricle, via either a unipolar orbipolar electrode. Single-chamber pacemakers can operate in either atriggered mode or a demand mode. In a triggered mode, a stimulationpulse is delivered to the desired heart chamber at the end of a definedtime-out interval to cause depolarization of the heart tissue(myocardium) and it's contraction. The stimulating pulse must be ofsufficient energy to cause depolarization of the heart chamber, acondition known as “capture.” The lowest pulse energy required toachieve capture is termed “threshold.” The pacemaker also delivers astimulation pulse in response to a sensed event arising from thatchamber when operating in a triggered mode.

When operating in a demand mode, sensing and detection circuitry allowfor the pacemaker to detect if an intrinsic cardiac depolarization,either an R-wave or a P-wave, has occurred within the defined time-outinterval. If an intrinsic depolarization is not detected, a pacing pulseis delivered at the end of the time-out interval. However, if anintrinsic depolarization is detected, the pacing pulse output isinhibited to allow the natural heart rhythm to preside. The differencebetween a triggered and demand mode of operation is the response of thepacemaker to a detected native event.

Dual chamber pacemakers are now commonly available and can provideeither trigger or demand type pacing in both an atrial chamber and aventricular chamber, typically the right atrium and the right ventricle.Both unipolar or bipolar dual chamber pacemakers exist in which aunipolar or bipolar lead extends from an atrial channel of the dualchamber device to the desired atrium (e.g. the right atrium), and aseparate unipolar or bipolar lead extends from a ventricular channel tothe corresponding ventricle (e.g. the right ventricle). In dual chamber,demand-type pacemakers, commonly referred to as DDD pacemakers, eachatrial and ventricular channel includes a sense amplifier to detectcardiac activity in the respective chamber and an output circuit fordelivering stimulation pulses to the respective chamber.

If an intrinsic atrial depolarization signal (a P-wave) is not detectedby the atrial channel, a stimulating pulse will be delivered todepolarize the atrium and cause contraction. Following either a detectedP-wave or an atrial pacing pulse, the ventricular channel attempts todetect a depolarization signal in the ventricle, known as an R-wave. Ifno R-wave is detected within a defined atrial-ventricular interval (AVinterval or delay), a stimulation pulse is delivered to the ventricle tocause ventricular contraction. In this way, rhythmic dual chamber pacingis achieved by coordinating the delivery of ventricular output inresponse to a sensed or paced atrial event.

Mounting clinical evidence supports the evolution of more complexcardiac stimulating devices capable of stimulating three or even allfour heart chambers to stabilize arrhythmias or to re-synchronize heartchamber contractions (Ref: Cazeau S. et al., “Four chamber pacing indilated cardiomyopathy,” Pacing Clin. Electrophsyiol 1994 17(11 Pt2):1974-9). Stimulation of multiple sites within a heart chamber hasalso been found effective in controlling arrhythmogenic depolarizations(Ref: Ramdat-Misier A., et al., “Multisite or alternate site pacing forthe prevention of atrial fibrillation,” Am. J. Cardiol., 199911;83(5b):237D-240D).

In order to achieve multi-chamber or multi-site stimulation in aclinical setting, conventional dual-chamber pacemakers have now beenused in conjunction with adapters that couple together two leads goingto different pacing sites or heart chambers. Reference is made to U.S.Pat. No. 5,514,161 to Limousin in which a triple chamber cardiacpacemaker, with the right and left atrial combined with a rightventricular lead, is described. Cazeau et al. (Pacing Clin.Electrophsyiol 1994 17(11 Pt 2):1974-9) describe a four chamber pacingsystem in which unipolar right and left atrial leads are connected via abifurcated bipolar adapter to the atrial port of a bipolar dual chamberpacemaker. Likewise, unipolar right and left ventricular leads areconnected via a bifurcated bipolar adapter to the ventricular channel.The left chamber leads were connected to the anode terminals and theright chamber leads were connected to the cathode terminals of the dualchamber device. In this way, simultaneous bi-atrial or simultaneousbi-ventricular pacing is achieved via bipolar stimulation but withseveral limitations.

Firstly, this configuration of bipolar stimulation is distinctlydifferent from a conventional bipolar lead configuration wherein boththe cathode and anode are located a short distance apart, approximatelyone centimeter, on the same lead. In the bi-chamber pacing configurationdescribed above, the anode and cathode are in fact located on twodifferent leads positioned in two different locations, severalcentimeters apart. In addition, since the tip electrode of one lead isforced to be the anode, and this has a significantly smaller surfacearea than the anode of a classic bipolar lead, the relative resistanceor impedance is higher with this lead system. In such a bipolar,bi-chamber pacing configuration, the threshold energy is likely to berelatively higher than in conventional bipolar stimulation in partbecause of the higher impedance of the electrode system. In addition,the electrode used for stimulation in the left heart chamber is usuallywithin the coronary sinus or a cardiac vein, not making direct contactwith the myocardium. As such, the energy needed to accommodatebi-chamber stimulation will usually be higher than that which iscommonly required for single chamber stimulation using bipolar leads.

A potential risk that exists when higher output settings are used, asmay be needed to ensure bi-chamber stimulation, is cross-chambercapture, also known as cross-stimulation (Ref: Levine P A, et al.,Cross-stimulation: the unexpected stimulation of the unpaced chamber,PACE 1985: 8: 600-606). If bi-atrial stimulation is delivered in abipolar configuration across one electrode located in the right atriumand another electrode located in the left atrium, which in actuality isthe coronary sinus which lies between the left atrium and leftventricle, the stimulation energy could conceivably be high enough toinadvertently capture one or both ventricles simultaneously. Suchcross-chamber capture is a highly undesirable situation in that theupper and lower chambers would contract against each other causingsevere cardiac output perturbation. This is also likely to occur withbipolar bi-ventricular stimulation with respect to cross-stimulation ofthe atrial chambers if the left ventricular lead located within acardiac vein is in close anatomic proximity to the left atrium and highoutputs are required to assure capture.

Another limitation of the multi-chamber stimulation systems describedabove is that simultaneous stimulation of left and right chambers, asrequired when two leads are coupled together by one adapter, is notalways necessary nor desirable. For example, in some patients conductionbetween the two atria may be compromised, however the pacemakingfunction of the sinus node in the right atrium may still be normal.Hence, detection of an intrinsic depolarization in the right atriumcould be used to trigger delivery of a pacing pulse in the left atrium.Since an intrinsic depolarization has occurred in one chamber,simultaneous stimulation of both chambers in this situation isunnecessary.

In another example, when inter-atrial or inter-ventricular conduction isintact, stimulation in one chamber may be conducted naturally todepolarize the second chamber. A stimulation pulse delivered in onechamber, using the minimum energy required to depolarize that chamber,will be conducted to the opposing chamber thus depolarizing bothchambers. In this case, stimulation of both chambers simultaneouslywould be wasteful of battery energy.

Another limitation is that, in the presence of an inter-atrial orinter-ventricular conduction defect, one may want to control theinterval between a sensed or paced event in one chamber and delivery ofa stimulation pulse to the other chamber. If pacing is required in bothchambers, the control of the sequence of the stimulation pulse deliveryto each chamber, rather than the simultaneous delivery of stimulationpulses, may be desirable in order to achieve a specific activationsequence that has hemodynamic benefit.

Yet another limitation is that, once implanted, the designation ofcathode and anode assignments is fixed and cannot be reassigned in orderto determine the polarity that results in the lowest stimulationthresholds, to achieve a desired directionality of the stimulationdelivery or to obtain the optimal sequencing of stimulation and/orsensing to optimize hemodynamic function. Typically, the electrode inthe right chamber is connected to the cathode terminal and the electrodein the left chamber is connected to the anode terminal. In other cases,the electrode in the left chamber is connected to the cathode terminalwhile the right chamber electrode is connected to the anode. In somepatients, a lower stimulation threshold or an improved excitationpattern or perhaps even hemodynamic benefit might be achieved byreversing the cathode and anode locations yet this cannot be donewithout operative intervention.

In the first generation of multi-chamber devices, an adapter wasrequired to connect multiple leads to a conventional dual chamberdevice, a requirement that adds cost and time to the implant procedure.Adapters can be cumbersome and an additional site for potential leadbreakage or discontinuity, essentially adding bulk and a “weak link” tothe implanted system. In certain current devices, adapters are no longerrequired. The connection between leads is hardwired internally in theconnector block coupling the ventricular leads to the ventricularchannel and the atrial leads to the atrial channel. While this designadvantageously eliminates the need for adapters, the hardwireconnections preclude the potential to non-invasively adjust the polarityorientation. This also prevents introducing separate timing betweenstimulation pulses delivered to each chamber or responding with anyprogrammable delays to a sensed event by delivery of an output pulse tothe other chamber.

To address some of these limitations, Verboven-Nelissen proposes amethod and apparatus that includes a multiple-chamber electrodearrangement having at least two electrodes placed to sense and/or pacedifferent chambers or areas of the heart. Reference is made to U.S. Pat.No. 5,720,518. The proposed method involves switching from a bipolar toa unipolar configuration during sensing for determining the originationsite of a detected depolarization signal. If the signal is determined tohave arisen from the SA node in the right atrium, a conduction intervalis applied to allow the cardiac signal to properly propagate to theother heart chambers. If no cardiac signal is detected in anothercardiac chamber, for example, the left atrium, then pacing is initiatedin that chamber at the end of the conduction interval. In this example,the interval is equal to the inter-atrial conduction time (i.e. the timerequired for a P-wave cardiac signal to propagate from right atrium toleft atrium). However the inter-atrial conduction time may vary overtime and the time for an excitation pulse to propagate from the rightchamber to the left chamber may be different than the propagation timefrom the left chamber to the right chamber. In addition, the conductiontime from the right atrium to the left atrium may vary from thatrequired to go from the left atrium to the right atrium. Depending onthe site of origin of the detected depolarization, it may behemodynamically beneficial to control the coupling interval between thedetected depolarization and the triggered output to the other chamber.U.S. Pat. No. 5,720,518 does not address the ability to control theinterval between detection and stimulation within the atria orventricles in the setting of multisite stimulation.

Reference is also made to U.S. Pat. No. 5,902,324 to Thompson et al. inwhich a multi-channel pacing system having two, three or four pacingchannels, each including a sense amplifier and pace output pulsegenerator, is described. A pacing pulse or detection of a spontaneousdepolarization in one of the right or left heart chambers is followed bya short conduction delay window. A pacing pulse that would otherwise bedelivered at the termination of the conduction delay window in theopposing heart chamber is inhibited if the conducted depolarization waveis sensed within the conduction delay window. While the duration of theconduction delay window can be programmed, no method is provided bywhich to select the optimal interval between chamber depolarizations.

Patients with marked hemodynamic abnormalities may benefit frommulti-site or multi-chamber pacing that controls the activation sequenceof the heart chambers. Precise control of the activation sequence mayimprove the coordination of heart chamber contractions resulting in moreeffective filling and ejection of blood from the heart. Patients withhemodynamic abnormalities often have conduction defects due to dilationof the heart or other causes. Yet, even in patients with intactconduction, precise control of the timing and synchronicity of heartchamber contractions may provide hemodynamic benefit.

There remains an unmet need, therefore, for a multi-chamber ormulti-site cardiac stimulation device that allows independentstimulation and sensing at multiple sites within the heart as well asflexible selection of stimulation sequence and timing intervals betweenthese stimulation sites. It would thus be desirable to provide amultisite or multichamber cardiac stimulation device having independentsensing and output circuitry for each pacing site. It would further bedesirable to allow flexible selection of sensing and stimulationpolarity for each stimulation site, including the designation of cathodeand anode assignment during bi-chamber stimulation. Further, it would bedesirable to provide flexible programming of the stimulation sequenceand timing intervals associated with multisite or multichamber pacing.Different timing intervals should be advantageously selectable dependingon the origination site of a detected depolarization wave or a desireddirectionality of depolarization in order to achieve optimal hemodynamicor electrophysiological benefit for the patient.

SUMMARY OF THE INVENTION

The present invention addresses this need by providing an implant ablemultichamber or multisite cardiac stimulation device in which theelectrode configurations for sensing and stimulation are flexiblyprogrammable, and the stimulation sequence between multiple sites can beprecisely controlled.

One aspect of the present invention is to provide a plurality ofconnection ports, preferably two through four connection ports, thatallow independent connection to the stimulation device of eachelectrical lead associated with a particular stimulation site in theheart. Each connection port further provides a unique terminal formaking electrical contact with only one electrode such that no twoelectrodes are required to be electrically coupled. Furthermore, eachelectrode, whether residing on a unipolar, bipolar or multipolar lead,may be selectively connected or disconnected through programmableswitching circuitry that determines the electrode configurations to beused for sensing and for stimulating at each stimulation site.

Another aspect of the present invention is a unique sensing circuitassociated with each stimulation site such that depolarizationsoccurring at each stimulation site can be detected independently ofevents occurring at other sites within the heart. This independentsensing advantageously allows the location of a detected depolarizationto be recognized by the stimulation device. The desired electrodes to beused for sensing in a specific heart chamber or at a specific sitewithin a heart chamber are connected to the input of the sensing circuitvia programmable switching circuitry.

Still another aspect of the present invention is a unique output circuitassociated with each stimulation site such that each site can bestimulated independently of other sites or on a precisely timed basistriggered by events occurring at other sites. The electrodes used forstimulation at a specific site may be different than those used forsensing at the same site.

Yet another aspect of the present invention is the ability to programunique coupling intervals for precisely controlling the activationsequence of stimulated sites. Coupling intervals may be defined inrelation to the originating location of a detected depolarization or inrelation to stimulus delivery at another location. Coupling intervalsare advantageously selected in a way that provides optimal hemodynamicbenefit to the patient by overcoming various conduction disorders orimproving coordination of heart chambers in patients suffering fromheart failure. One embodiment of the present invention includes a methodfor automatically determining the optimal coupling intervals andadjusting the programmed settings based on measurements related to thehemodynamic state of the heart.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention may be morereadily understood by reference to the following description taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a simplified, partly cutaway view illustrating an implant ablestimulation device in electrical communication with at least three leadsimplanted into a patient's heart for delivering multi-chamberstimulation and shock therapy;

FIG. 2 is a functional block diagram of the multi-chamber implant ablestimulation device of FIG. 1, illustrating the basic elements thatprovide pacing stimulation, cardioversion, and defibrillation in fourchambers of the heart;

FIG. 3 is a simplified, partly cutaway view illustrating an implant ablestimulation device in electrical communication with at least fourbipolar leads implanted into a patient's heart representing a preferredembodiment of the present invention;

FIG. 4 is a block diagram of the stimulation device of FIG. 3,illustrating a switch with four ports for connection to four leads;

FIG. 5 depicts a flow chart describing an overview of a method forautomatically configuring sensing electrodes for use in the cardiacstimulation device of the present invention;

FIGS. 6 through 9 depict flow chart describing a method forautomatically configuring stimulation electrodes for use in the cardiacstimulation device of the present invention; and

FIG. 10 is a flow chart describing an overview of a method implementedby the stimulation device of FIG. 2, for automatically adjusting thecoupling intervals used in the methods of FIGS. 5-9, to achieve anoptimal physiological response to a multichamber stimulation therapy.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of a best mode presently contemplated forpracticing the invention. This description is not to be taken in alimiting sense but is made merely for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe ascertained with reference to the issued claims. In the descriptionof the invention that follows, like numerals or reference designatorswill be used to refer to like parts or elements throughout.

The present invention relates to a cardiac stimulation device capable ofdelivering precisely ordered stimulation pulses to multiple chambers ofthe heart, referred to herein as multi-chamber stimulation, or tomultiple sites within a chamber of the heart, referred to herein asmulti-site stimulation. As used herein, the shape of the stimulationpulses is not limited to an exact square or rectangular shape, but mayassume any one of a plurality of shapes which is adequate for thedelivery of an energy packet or stimulus.

The stimulation device is intended for use in patients suffering fromhemodynamic dysfunction, which may or may not be accompanied byconduction disorders. Precisely controlled stimulation at multiple sitesor in multiple chambers is provided to intentionally make use of thepacing function of the heart in order to improve cardiac hemodynamics byre-coordinating heart chamber contractions and/or preventingarrhythmogenic depolarizations from occurring. Thus, the cardiacstimulation device is capable of delivering at least low-voltagestimulation pulses to multiple stimulation sites for providing pacingtherapy, and may include high-voltage stimulation shocks for providingcardioversion therapy and defibrillation therapy.

FIG. 1 illustrates a stimulation device 10 in electrical communicationwith a patient's heart 12 by way of three leads 20, 24 and suitable fordelivering multi-chamber stimulation and shock therapy. To sense rightatrial cardiac signals and to provide right atrial chamber stimulationtherapy, the stimulation device 10 is coupled to an implant able rightatrial lead 20 having at least an atrial tip electrode 22, whichtypically is implanted in the patient's right atrial appendage.

To sense left atrial and/or left ventricular cardiac signals and toprovide left-chamber pacing therapy, the stimulation device 10 iscoupled to a “coronary sinus” lead 24 designed for placement in the“coronary sinus region” via the coronary sinus os so as to place adistal electrode adjacent to the left ventricle and additionalelectrode(s) adjacent to the left atrium. As used herein, the phrase“coronary sinus region” refers to the vasculature of the left ventricle,including any portion of the coronary sinus, great cardiac vein, leftmarginal vein, left posterior ventricular vein, middle cardiac vein,and/or small cardiac vein or any other cardiac vein accessible by thecoronary sinus. It could also be an epicardial lead placed at the timeof thoracotomy or thorascopy.

Accordingly, the coronary sinus lead 24 is designed to receive atrialand/or ventricular cardiac signals and to deliver: left ventricularpacing therapy using at least a left ventricular tip electrode 26, leftatrial pacing therapy using at least a left atrial ring electrode 27,and shocking therapy using at least a left atrial coil electrode 28. Fora more detailed description of a coronary sinus lead, refer to U.S.patent application Ser. No. 09/196,898, titled “A Self-AnchoringCoronary Sinus Lead” (Pianca et. al), and U.S. Pat. No. 5,466,254,titled “Coronary Sinus Lead with Atrial Sensing Capability” (Helland)that are incorporated herein by reference.

The stimulation device 10 is also shown in electrical communication withthe patient's heart 12 by way of an implant able right ventricular lead30 having, in this embodiment, a right ventricular tip electrode 32, aright ventricular ring electrode 34, a right ventricular (RV) coilelectrode 36, and an SVC coil electrode 38. Typically, the rightventricular lead 30 is transvenously inserted into the heart 12 so as toplace the right ventricular tip electrode 32 in the right ventricularapex so that the RV coil electrode 36 will be positioned in the rightventricle and the SVC coil electrode 38 will be positioned in thesuperior vena cava.

Accordingly, the right ventricular lead 30 is capable of receivingcardiac signals, and delivering stimulation in the form of pacing andshock therapy to the right ventricle.

FIG. 2 illustrates a simplified block diagram of the multi-chamberimplant able stimulation device 10, which is capable of treating bothfast and slow arrhythmias with stimulation therapy, includingcardioversion, defibrillation, and pacing stimulation. While aparticular multi-chamber device is shown, this is for illustrationpurposes only, and one of skill in the art could readily duplicate,eliminate or disable the appropriate circuitry in any desiredcombination to provide a device capable of treating the appropriatechamber(s) with cardioversion, defibrillation and/or pacing stimulation.

The stimulation device 10 includes a housing 40 which is often referredto as “can”, “case” or “case electrode”, and which may be programmablyselected to act as the return electrode for all “unipolar” modes. Thehousing 40 may further be used as a return electrode alone or incombination with one or more coil electrodes 28, 36, or 38, for shockingpurposes. The housing 40 further includes a connector having a pluralityof terminals, 42, 44, 46, 48, 52, 54, 56, and 58 (shown schematicallyand, for convenience, the names of the electrodes to which they areconnected are shown next to the terminals). In accordance with thepresent invention, the connector will provide a unique connection portfor each lead in communication with the heart so as to avoid thenecessity of adapters. Furthermore, the connector will provide a uniqueterminal for electrical connection to each electrode(s) associated witheach stimulation site within the heart 12. In this way, coupling of morethan one stimulation site using adaptors, or hardwiring betweenterminals inside the connector, is avoided allowing independentstimulation and sensing at each stimulation site.

As such, in the embodiment of FIG. 2, the connector includes at least aright atrial tip terminal 42 adapted for connection to the atrial(A_(R)) tip electrode 22 in order to achieve right atrial sensing andpacing.

To achieve left chamber sensing, pacing and/or shocking, the connectorincludes at least a left ventricular (V_(L)) tip terminal 44, a leftatrial (A_(L)) ring terminal 46, and a left ventricular (V_(L)) shockingterminal (coil) 48, which are adapted for connection to the leftventricular tip electrode 26, the left atrial ring electrode 27, and theleft atrial coil electrode 28, respectively.

To support right ventricular sensing, pacing and/or shocking, theconnector further includes a right ventricular (V_(R)) tip terminal 52,a right ventricular (V_(R)) ring terminal 54, a right ventricular (RV)shocking terminal (coil) 56, and an SVC shocking terminal (coil) 58,which are adapted for connection to the right ventricular tip electrode32, right ventricular ring electrode 34, the RV coil electrode 36, andthe SVC coil electrode 38, respectively. Thus, the embodiment of FIG. 1includes one connection port for the right atrial lead 20 and twobipolar, high-voltage connection ports for the right ventricular lead 30and the coronary sinus lead 24, allowing sensing and stimulation in allfour chambers of the heart.

In alternative embodiments, the stimulation device 10 may include amulti-port connector capable of accommodating any combination of three,four or more uni-polar, bi-polar or multi-polar leads. The arrangementand type of leads used may vary depending on the type of stimulationtherapy to be delivered and individual patient need. In a preferredembodiment, to be described later in conjunction with FIG. 3, fourbipolar connection ports are provided to accommodate a programmableselection of unipolar, bipolar or combination stimulation and sensing inany or all four chambers of the heart, or at four sites within the heart12.

At the core of the stimulation device 10 is a programmablemicrocontroller 60 that controls the various modes of stimulationtherapy. As is well known in the art, the microcontroller 60 typicallyincludes a microprocessor, or equivalent control circuitry, designedspecifically for controlling the delivery of stimulation therapy, andmay further include RAM or ROM memory, logic and timing circuitry, statemachine circuitry, and I/O circuitry. Typically, the microcontroller 60includes the ability to process or monitor input signals (data) ascontrolled by a program code stored in a designated block of memory. Thedetails of the design and operation of the microcontroller 60 are notcritical to the present invention. Rather, any suitable microcontroller60 may be used that carries out the functions described herein. The useof microprocessor-based control circuits for performing timing and dataanalysis functions are well known in the art.

As shown in FIG. 2, an atrial pulse generator 70 and a ventricular pulsegenerator 72 generate pacing stimulation pulses for delivery by theright atrial lead 20, the right ventricular lead 30 and/or the coronarysinus lead 24, via the switch bank 74. It is understood that in order toprovide stimulation therapy in each of the four chambers of the heart,or at multiple sites within one or more chambers, the atrial pulsegenerator 70 and the ventricular pulse generator 72 include dedicated,independent pulse generators, multiplexed pulse generators, or sharedpulse generators. However, in order to provide independent stimulationat each stimulation site, atrial pulse generator 70 and ventricularpulse generator 72 include independent output circuits for eachstimulation site that allow delivery of unique stimulation pulses toeach site.

The atrial pulse generator 70 in FIG. 2 thus includes a right atrialoutput circuit for delivering stimulation pulses to the right atrium viaright atrial lead 20, and further includes a left atrial output circuitfor delivering stimulation pulses to the left atrium via coronary sinuslead 24. The ventricular pulse generator 72 includes a right ventricularoutput circuit for delivering stimulation pulses to the right ventriclevia right ventricular lead 30, and further includes a left ventricularoutput circuit for delivering stimulation pulses to the left ventriclevia the coronary sinus lead 24. The atrial pulse generator 70 and theventricular pulse generator 72 are controlled by the microcontroller 60via appropriate control signals 76 and 78, respectively, to trigger orinhibit the stimulation pulses.

The microcontroller 60 further includes timing control circuitry 79which is used to control the timing of such stimulation pulses (e.g.pacing rate, atrio-ventricular (AV) delay, interatrial conduction (A-A)delay, or interventricular conduction (V-V) delay, etc.), as well as tokeep track of the timing of refractory periods, PVARP intervals, noisedetection windows, evoked response windows, alert intervals, markerchannel timing, etc.

In accordance with one embodiment of the present invention, the timingcontrol circuitry 79 is also used to control coupling intervals, whichprecisely control the stimulation sequence during multi-chamber ormulti-site stimulation. For example, the interatrial conduction (A-A)delay may be determined by programmable selection of coupling intervalsdefined according to whether an intrinsic atrial depolarization is firstsensed in the right atrium or in the left atrium. A right-to-left atrialcoupling interval may be programmed to control the time between a rightatrial detected event (P-wave) and the delivery of a left atrialstimulation pulse. A different left-to-right atrial coupling intervalmay be programmed to control the time between a left atrial detectedP-wave and right atrial stimulation pulse delivery.

Furthermore, different coupling intervals may be defined in relation topaced events than detected events. Hence, the coupling interval betweena right atrial paced event and a left atrial paced event may bedifferent than the coupling interval between a right atrial detectedevent (intrinsic P-wave) and a left atrial paced event. In other words,for each stimulation site, a unique coupling interval between it and allother stimulation sites may be defined in relation to both paced eventsand detected events occurring at that site. Details regarding theapplication of coupling intervals as provided by the present inventionwill be described later in conjunction with FIGS. 5 through 10.

The switch bank 74 includes a plurality of switches for connecting thedesired electrodes to the appropriate I/O circuits, thereby providingcomplete electrode programmability. Accordingly, the switch bank 74, inresponse to a control signal 80 from the microcontroller 60, determinesthe polarity of the stimulation pulses (e.g. unipolar, bipolar, combinedmanner, etc.) by selectively closing the appropriate combination ofswitches (not shown).

In addition to providing programmable stimulation polarity, thestimulation device 10 includes the programmable polar assignments ofeach electrode during bipolar or unipolar stimulation. For example,bi-ventricular stimulation may be provided in a combined manner betweenthe right ventricular tip electrode 32 and left ventricular tipelectrode 26 by connecting these two tip electrodes to ventricular pulsegenerator 72 via switch bank 74.

The stimulation device 10 provides the programmable assignment ofcathode and anode poles in the following stimulation configuration. Theleft ventricular tip electrode 26 may be selected as the cathode withthe right ventricular tip electrode 32 selected as the anode, to achieveone directionality and stimulation threshold. Alternatively, the leftventricular tip electrode 26 may be selected as the anode and the rightventricular tip electrode 32 may be selected as the cathode, to achievea different directionality and stimulation threshold. In this way, theselection of cathode and anode assignments during bi-atrial orbi-ventricle stimulation, or within a chamber during multisitestimulation, may be tailored to meet the individual patient's need.

In some patients it may be advantageous to provide anodal stimulationrather than cathodal stimulation. Hence, it is one feature of thepresent invention to further allow assignment of the active electrodeused in unipolar stimulation to be the anode with the housing 40assigned as the cathode. For example, unipolar anodal stimulation of theright ventricle may be achieved by designating the right ventricularring electrode 54 as the anode and the housing 40 as the cathode.

The programmable designation of electrode poles is preferablyaccomplished via electronic switching devices controlled by logic gatesreceiving high or low signals under the control of microprocessor 60.For details regarding a switching circuitry that may be used forproviding programmable selection of stimulation and sensing electrodeconfigurations, refer to U.S. Pat. No. 4,991,583 to Silvian, herebyincorporated herein by reference.

Atrial sensing circuit 82 and ventricular sensing circuit 84 may also beselectively coupled to the right atrial lead 20, coronary sinus lead 24,and the right ventricular lead 30, through the switch bank 74, fordetecting the presence of cardiac activity in each of the four chambersof the heart. In order to detect events occurring within each chamber orat each stimulation site independently, the atrial and ventricularsensing circuits 82 and 84 include dedicated independent senseamplifiers associated with each stimulation site within the heart 12. Asused herein, each of the atrial sensing circuit 82 and the ventricularsensing circuit 84 includes a discriminator, which is a circuit thatsenses and can indicate or discriminate the origin of a cardiac signalin each of the cardiac chambers.

The inputs to each sense amplifier are programmable and may be selectedin any combination of available electrode terminals in order to provideindependent unipolar or bipolar sensing at each stimulation site. Inthis way, a detected atrial event may be distinguished as being a rightatrial event or a left atrial event. Likewise, a detected ventricularevent may be distinguished as a right ventricular event or a leftventricular event.

If the stimulation device 10 is being used for multisite stimulationwithin a chamber of the heart, one electrode might be positioned in theupper area of the chamber and a second electrode might be positioned ina lower area of the same chamber or any two distinct locations withinthat chamber. Unique sensing circuitry for each electrode allowsdiscrimination of a detected event as occurring in either the upper areaor the lower area of the chamber. The stimulation response provided bythe device 10 may then be determined based on the location of a detectedevent.

Additionally, combination sensing for bi-atrial or bi-ventricularsensing during multichamber stimulation or combipolar sensing within asingle chamber during multisite stimulation may be selected byprogramming the appropriate inputs to the individual sense amplifiers.The switch bank 74 determines the “sensing polarity” of the cardiacsignal by selectively closing the appropriate switches. In this way, theclinician may program the sensing polarity independent of thestimulation polarity.

Each of the atrial sensing circuit 82 or the ventricular sensing circuit84 preferably employs one or more low power, precision amplifiers withprogrammable gain and/or automatic gain control, bandpass filtering, anda threshold detection circuit, to selectively sense the cardiac signalof interest. The automatic gain control enables the stimulation device10 to deal effectively with the difficult problem of sensing the lowamplitude signal characteristics of atrial or ventricular fibrillation.The outputs of the atrial and ventricular sensing circuits 82 and 84 areconnected to the microcontroller 60 for triggering or inhibiting theatrial and ventricular pulse generators 70 and 72, respectively, in ademand fashion, in response to the absence or presence of cardiacactivity, respectively, in the appropriate chambers of the heart.

One feature of the present invention is to provide precise control ofthe activation sequence of the stimulation sites. To this end, thestimulation device 10 may act only in a trigger mode thereby gainingcomplete control of the heart rhythm in an attempt to provide a morehemodynamically effective contraction sequence of the heart chambersthan that produced by the natural heart rhythm.

Preferably, the stimulation device 10 operates in a trigger mode incontrolling the timing of contraction at all the stimulation sites.Alternatively, it may operate in a demand mode in delivering orinhibiting stimulation pulses to at least one site, and may operate in atrigger mode in delivering stimulation pulses to all other stimulationsites. For example, atrial pulse generator 70 may be inhibited fromdelivering a right atrial stimulation pulse when atrial sensing circuit82 detects an intrinsic P-wave in the right atrium within a given escapeinterval. However, this detection may cause microcontroller 60 totrigger atrial pulse generator 70 and ventricular pulse generator 72 todeliver stimulation pulses at prescribed intervals of time to the leftatrium and the right and left ventricles, respectively, regardless ofany events detected in these chambers. In this way, the activationsequence of all four heart chambers is precisely controlled by thenatural pacemaking activity of the sinus node. Hence, in the presentinvention, the pacing mode of stimulation device 10, that is demand ortrigger mode, for each stimulation site is preferably programmable.

If the cardiac stimulation device 10 is also intended for deliveringcardioversion and defibrillation therapy, arrhythmia detection by thestimulation device 10 utilizes the atrial and ventricular sensingcircuits 82 and 84 to sense cardiac signals, for determining whether arhythm is physiologic or pathologic. As used herein “sensing” isreserved for the noting of an electrical signal, and “detection” is theprocessing of these sensed signals and noting the presence of anarrhythmia. The timing intervals between sensed events (e.g. P-waves,R-waves, and depolarization signals associated with fibrillation whichare sometimes referred to as “F-waves” or “Fib-waves”) are thenclassified by the microcontroller 60 by comparing them to a predefinedrate zone limit (e.g. bradycardia, normal, low rate VT, high rate VT,and fibrillation rate zones) and various other characteristics (e.g.sudden onset, stability, physiologic sensors, and morphology, etc.) inorder to determine the type of remedial therapy that is needed (e.g.bradycardia pacing, anti-tachycardia pacing, cardioversion shocks ordefibrillation shocks, collectively referred to as “tiered therapy”).

Cardiac signals are also applied to the inputs of an analog-to-digital(A/D) data acquisition system 90. The data acquisition system 90 isconfigured to acquire intracardiac electrogram (EGM) signals, convertthe raw analog data into digital signals, and store the digital signalsfor later processing and/or telemetric transmission to an externaldevice 102. The data acquisition system 90 is coupled to the rightatrial lead 20, the coronary sinus lead 24, and the right ventricularlead 30 through the switch bank 74 to sample cardiac signals across anypair of desired electrodes.

The microcontroller 60 is further coupled to a memory 94 by a suitabledata/address bus 96, wherein the programmable operating parameters usedby the microcontroller 60 are stored and modified, as required, in orderto customize the operation of the stimulation device 10 to suit theneeds of a particular patient. Such operating parameters define, forexample, pacing pulse amplitude, pulse duration, electrode polarity,rate, sensitivity, automatic features, arrhythmia detection criteria,and the amplitude, wave shape and vector of each shocking pulse to bedelivered to the patient's heart 12 within each respective tier oftherapy.

Advantageously, the operating parameters of the stimulation device 10may be non-invasively programmed into the memory 94 through a telemetrycircuit 100 in telemetric communication with the external device 102,such as a programmer, transtelephonic transceiver, or a diagnosticsystem analyzer. The telemetry circuit 100 is activated by themicrocontroller 60 by a control signal 106. The telemetry circuit 100advantageously allows intracardiac electrograms and status informationrelating to the operation of the stimulation device 10 (as contained inthe microcontroller 60 or memory 94) to be sent to the external device102 through the established communication link 104.

The stimulation device 10 may further include a physiologic sensor 108,commonly referred to as a “rate-responsive” sensor because it istypically used to adjust pacing stimulation rate according to theexercise state of the patient. However, the physiological sensor 108 mayfurther be used to detect changes in cardiac output, changes in thephysiological condition of the heart, or diurnal changes in activity(e.g. detecting sleep and wake states). Accordingly, the microcontroller60 responds by adjusting the various pacing parameters (such as rate, AVDelay, V-V Delay, etc.) at which the atrial and ventricular pulsegenerators 70 and 72 generate stimulation pulses.

In accordance with one feature of the present invention, couplingintervals that determine the activation sequence of stimulated chambersor sites, may be adjusted based on changes detected by the physiologicsensor 108. Preferably physiologic sensor 108 includes detection ofchanges related to the hemodynamic state of the patient and therebyallows adjustment of the coupling intervals to be made in a way thatoptimizes the hemodynamic response to multisite or multichamberstimulation. One method for accomplishing automatic adjustment ofcoupling intervals based on physiologic sensor 108 data will bedescribed in detail in conjunction with FIG. 10.

While the physiologic sensor 108 is shown as being included within thestimulation device 10, it is to be understood that the physiologicsensor 108 may alternatively be external to the stimulation device 10,yet still be implanted within, or carried by the patient. A common typeof rate responsive sensor is an activity sensor, such as anaccelerometer or a piezoelectric crystal, which is mounted within thehousing 40 of the stimulation device 10. Other types of physiologicsensors are also known, for example, sensors which sense the oxygencontent of blood, cardiac output, respiration rate and/or minuteventilation, pH of blood, ventricular gradient, etc. However, any sensormay be used which is capable of sensing a physiological parameter, whichcorresponds to the exercise or hemodynamic state of the patient.

The stimulation device 10 additionally includes a power source such as abattery 110 that provides operating power to all the circuits shown inFIG. 2. For the stimulation device 10, which employs shocking therapy,the battery 110 must be capable of operating at low current drains forlong periods of time, and also be capable of providing high-currentpulses (for capacitor charging) when the patient requires a shock pulse.The battery 110 must preferably have a predictable dischargecharacteristic so that elective replacement time can be detected.Accordingly, the stimulation device 10 can employ, for example,lithium/silver vanadium oxide batteries.

As further shown in FIG. 2, the stimulation device 10 is shown as havingan impedance measuring circuit 112 which is enabled by themicrocontroller 60 by a control signal 114. The known uses for animpedance measuring circuit 120 include, but are not limited to, leadimpedance surveillance during the acute and chronic phases for assessingthe mechanical integrity of the lead; detecting operable electrodes andautomatically switching to an operable pair if mechanical disruptionoccurs in one lead; measuring respiration or minute ventilation;detecting when the device has been implanted; and a variety ofhemodynamic variables such as measuring stroke volume; and detecting theopening of the valves, etc. The impedance measuring circuit 120 isadvantageously coupled to the switch bank 74 so that any desiredelectrode may be used.

The impedance measuring circuit 112 may be used advantageously in thepresent invention for monitoring hemodynamic indicators, such asventricular impedance as an indication of cardiac output, to providefeedback in the selection of optimal coupling intervals. Impedancemeasuring circuit 112 may be used alone or in conjunction withphysiological sensor 108 for providing such feedback. This data may beperiodically stored in memory 94 such that a physician may then accessthis data during patient follow-up visits to obtain useful informationin manually selecting and programming coupling intervals. Preferably,this data may be used by the stimulation device 10 to automaticallyadjust coupling intervals as will be described in conjunction with FIG.10.

In cases where a primary function of the stimulation device 10 is tooperate as an implant able cardioverter/defibrillator (ICD) device, itmust detect the occurrence of an arrhythmia, and automatically apply anappropriate antitachycardia pacing (ATP) and/or electrical shock therapyto the heart aimed at terminating the detected arrhythmia. To this end,the microcontroller 60 further controls a shocking circuit 116 by way ofa control signal 118. The shocking circuit 116 generates shocking pulsesof low (up to 0.5 Joules), moderate (0.5-10 Joules), or high (11 to 40Joules) energy, as controlled by the microcontroller 60. Such shockingpulses are applied to the patient's heart through at least two shockingelectrodes, and as shown in this embodiment, selected from the leftatrial coil electrode 28, the RV coil electrode 36, and/or the SVC coilelectrode 38 (FIG. 1). As noted earlier, the housing 40 may act as anactive electrode in combination with the RV electrode 36, or as part ofa split electrical vector using the SVC coil electrode 38 or the leftatrial coil electrode 28 (i.e., using the RV electrode as commonelectrode).

Cardioversion shocks are generally considered to be of low to moderateenergy level (so as to minimize pain felt by the patient), and/orsynchronized with an R-wave and/or pertaining to the treatment oftachycardia. Defibrillation shocks are generally of moderate to highenergy level (i.e., corresponding to thresholds in the range of 5-40Joules), delivered asychronously (since R-waves may be toodisorganized), and pertaining exclusively to the treatment offibrillation. Accordingly, the microcontroller 60 is capable ofcontrolling the synchronous or asynchronous delivery of the shockingpulses.

FIG. 3 illustrates a preferred embodiment of the present inventionshowing one bipolar lead 20 implanted in the right atrium, one bipolarlead 21 implanted in the coronary sinus region adjacent to left atrium,one bipolar high-voltage lead 30 implanted in the right ventricle, andanother bipolar high-voltage lead 31 implanted in the coronary sinusregion adjacent to the left ventricle. Using this electrodeconfiguration with the stimulation device 10, independent unipolar orbipolar stimulation and sensing of either or both atria is possible, or,alternatively, combination bi-atrial stimulation or sensing can beperformed with the cathode and anode assignments applied to the rightatrial tip electrode 22, right atrial ring electrode 23, left atrialring electrode 27, and left atrial tip electrode 29 as desired.

In addition, independent unipolar or bipolar stimulation and sensing anbe provided separately in the right and left ventricles or,alternatively, combination bi-ventricular stimulation or sensing can beperformed with the cathode and anode assignments applied to the rightventricular tip electrode 32, right ventricular ring electrode 34, leftventricular ring electrode 25, and left ventricular tip electrode 26 asdesired.

In this embodiment, and as further illustrated in FIG. 4, thestimulation device 10 of FIG. 3 includes four bipolar connection ports200, 210, 220 and 230. A left ventricular connection port (LV connectionport) 200 accommodates the left ventricular lead (LV lead) 24 withterminals 44, 45, 48 that are associated with the left ventricular tipelectrode (LV tip electrode) 26, the left ventricular ring electrode (LVring electrode) 25, and the left atrial coil electrode (LA coilelectrode) 28, respectively.

A left atrial connection port (LA connection port) 210 accommodates theleft atrial lead (LA lead) 21 with terminals 49, 47 that are associatedwith the left atrial tip electrode (LA tip electrode) 29 and the leftatrial ring electrode (LA ring electrode) 27, respectively. A rightventricular connection port (RV connection port) 220 accommodates theright ventricular lead (RV lead) 30 with terminals 52, 54, 56, 58 thatare associated with the right ventricular tip electrode (RV tipelectrode) 32, the right ventricular ring electrode (RV ring electrode)34, the right ventricular coil electrode (RVCE) 36 and the rightventricular SVC coil electrode (RV SVC coil electrode) 38, respectively.A right atrial connection port (RA connection port) 230 accommodates theright atrial lead (RA lead) 20 with terminals that are associated withthe right atrial tip electrode (RA tip electrode) 22 and the rightatrial ring electrode (RA ring electrode) 23, respectively.

It is recognized that numerous variations exist in which combinations ofunipolar, bipolar and/or multipolar leads may be positioned at desiredlocations within the heart in order to provide multichamber or multisitestimulation. The present invention provides for the flexibility ofindependent stimulation and/or sensing at multiple sites by providing acardiac stimulation device that includes multiple connection ports withunique terminals for the electrode(s) associated with each stimulationsite as well as independent sensing and output circuitry for eachstimulation site. As such, stimulation and sensing sites are notobligatorily coupled together by adapters or hardwiring within thestimulation device that would otherwise preclude independent sensing andstimulation at each pacing site during either multichamber or multisitepacing.

FIGS. 5 and 6 illustrate a flow chart describing methods of operation200 and 300, respectively, that are implemented in one embodiment of thestimulation device 10 in which defined coupling intervals are applied bymicrocontroller 60 for controlling the sequence of stimulation pulsedelivery by the atrial pulse generator 70 and the ventricular pulsegenerator 72. In this flow chart, and the other flow charts describedherein, the various algorithmic steps are summarized in individual“blocks”. Such blocks describe specific actions or decisions that mustbe made or carried out as the algorithm proceeds. Where amicrocontroller (or equivalent) is employed, the flow charts presentedherein provide the basis for a “control program” that may be used bysuch a microcontroller (or equivalent) to effectuate the desired controlof the stimulation device. Those skilled in the art may readily writesuch a control program based on the flow charts and other descriptionspresented herein.

The methods 200 and 300 will be described in relation to the implantconfiguration of FIG. 3, where sensing and pacing are performed in theright atrium, left atrium, right ventricle and left ventricle. It isrecognized that the algorithmic steps illustrated in FIGS. 5 and 6 mayeasily be modified to control the stimulation sequence during anymulti-chamber or multi-site stimulation configuration.

At the time of implant, coupling intervals are programmed by thephysician to precisely control the activation sequence of all fourchambers whenever pacing is required. Default nominal values stored inthe stimulation device 10 may also be selected. Coupling intervals aredefined in association with paced and sensed events occurring at eachstimulation site. For example, the delivery of a right atrialstimulation pulse by the atrial pulse generator 70 will causemicrocontroller 60 to initiate three coupling intervals: one associatedwith the left atrium; another associated with the right ventricle; andyet another associated with the left ventricle. These coupling intervalscontrol the time between the delivery of the right atrial stimulationpulse and the delivery of the left atrial, right ventricular, and leftventricular stimulation pulses, respectively.

Likewise, the detection of a P-wave in the right atrium by the atrialsense circuitry 82 will also cause microcontroller 60 to initiate threecoupling intervals associated with the left atrium, right ventricle, andleft ventricle. However, these coupling intervals may be different thanthe coupling intervals initiated due to a right atrial paced event.Similarly, left atrial coupling intervals are defined for the case of aleft atrial event being detected before a right atrial event forcontrolling the time between the left atrial detection and right atrialstimulation, right ventricular stimulation and left ventricularstimulation. In addition, the system can be configured to deliver theleft atrial stimulus before the right atrial stimulus, or the leftventricular stimulus before the right ventricular stimulus.

The method 200 and 300 of FIGS. 5 and 6 represent the application ofthese coupling intervals over one cardiac cycle. It is assumed in thisexample, that the stimulation device 10 is programmed to operate in ademand mode in the atrial channels and in a triggered mode in theventricular channels although, it can be set to operate in the triggeredmode in both the atrium and ventricle or the triggered mode in theatrium and the demand mode in the ventricle.

Starting at step 202, a new escape interval is initiated. The length ofthis escape interval is determined by the programmed base pacing (orstimulation) rate. For example, if the base pacing rate is programmed tobe 60 beats per minute, then the escape interval is 1000 msec. Method200 waits for the detection of an intrinsic P-wave by atrial sensecircuit 82 prior to expiration of the escape interval.

If at decision step 204 the method 200 determines that the escapeinterval has expired before an intrinsic P-wave is detected,microprocessor 60 triggers the right atrial output circuitry in theatrial pulse generator 70 to deliver a stimulation pulse to the rightatrium at step 206, according to the programmed electrode configurationfor stimulation in the right atrium.

The delivery of a right atrial stimulation pulse causes microprocessor60 to trigger timing control circuitry 79 to start three separate timerssimultaneously at step 208. As it is illustrated in FIG. 7, one timerinitiates a right atrial pace to left atrium (RApace to LA) couplinginterval at step 325. Another timer initiates a right atrial pace toright ventricle (RApace to RV) coupling interval at step 335. The thirdtimer simultaneously initiates a right atrial pace to left ventricle(RApace to LV) coupling interval at step 345. Upon expiration of thecoupling intervals, the stimulation device 10 delivers the requiredstimulation pulses at step 310.

FIG. 7 illustrates further details of step 310. Upon expiration of theright atrial pace to left atrium (RApace to LA) coupling interval (step325), method 300 inquires, at decision step 326, if an intrinsic leftatrial depolarization (P-wave) is detected. If it is, method 300inhibits the delivery of a left atrial stimulation pulse at step 328. Ifan intrinsic left atrial depolarization is not detection at step 326,the microcontroller 60 triggers the left atrial output circuitry ofatrial pulse generator 70 to deliver a left atrial (LA) stimulationpulse at step 327.

Similarly, upon expiration of the right atrial pace to left atrium(RApace to RV) coupling interval at step 335, method 300 inquires, atdecision step 336, if an intrinsic right ventricular depolarization(R-wave) is detected. If it is, method 300 inhibits the delivery of aright ventricular stimulation pulse at step 338. If an intrinsic rightventricular depolarization is not detection at step 336, themicrocontroller 60 triggers the right atrial output circuitry of theventricular pulse generator 72 to deliver a right ventricular (RV)stimulation pulse at step 337.

In a similar manner, upon expiration of the right atrial pace to leftventricle (RApace to LV) coupling interval at step 345, method 300inquires, at decision step 346, if an intrinsic left ventriculardepolarization (R-wave) is detected. If it is, method 300 inhibits thedelivery of a left ventricular stimulation pulse at step 348. If anintrinsic left ventricular depolarization is not detected at step 346,the microprocessor 60 triggers the left atrial output circuitry of theventricular pulse generator 72 to deliver a left ventricular (LV)stimulation pulse at step 347.

With respect to steps 328, 338, and 348, if a sensed event occurs on theatrial channel or the ventricular channel, method 300 detects thechamber in which the sensed event originated and the times the deliveryof the output pulse to the other chamber in accord with the automatic orphysician set interval.

After the expiration of all these three coupling intervals and thedelivery of triggered stimulation to the designated stimulation sites,method 300 returns to step 202 where the microprocessor 60 initiates anew escape interval to start the next cardiac pacing cycle.

Returning now to FIGS. 5 and 6, if a P-wave is detected by the atrialsense circuitry 82 prior to the expiration of the escape interval atdecision step 204, methods 200 and 300 determine, at decision step 216,if this detection has been made by the right atrial sensing circuitry orthe left atrial sensing circuitry of the atrial sense circuit 82.

If a P-wave is detected at step 204 and the microprocessor 60 determinesthat the P-wave has been detected in the left atrial sense circuitry ofatrial sense circuitry 82 at decision step 216, then the couplingintervals associated with a left atrial sense event are initiated bytiming the control circuitry 79 at step 217. As it is illustrated inFIG. 8, a left atrial sense to right atrial (LAsense to RA) couplinginterval is initiated in one timer at step 425. This coupling intervalmay or may not be equal to the coupling interval between the right andleft atria associated with a detected right atrial event.

On a separate timer, the timing control circuitry 79 simultaneouslyinitiates a left atrial sense to right ventricle (LAsense to RV)coupling interval at step 435. Another timer starts the left atrialsense to left ventricle (LAsense to LV) coupling interval at step 445.If a sensed event occurs within the designated coupling intervals, thetiming of the stimulus output to the other chamber is based on thesensed event and not the output pulse in the atrium. Upon expiration ofthe coupling intervals, the stimulation device 10 delivers the requiredstimulation pulses at step 318.

FIG. 8 illustrates further details of step 318. Upon expiration of theleft atrial sense to right atrial (LAsense to RA) coupling interval atstep 425, method 300 inquires, at decision step 426, if an intrinsicright atrial depolarization (P-wave) is detected. If it is, method 300inhibits the delivery of a right atrial stimulation pulse at step 428.If an intrinsic left atrial depolarization is not detection at step 426,the microprocessor 60 triggers the right atrial output circuitry of theatrial pulse generator 70 to deliver a stimulation pulse to the rightatrium at step 427.

Similarly, upon expiration of the left atrial to right ventricular(LAsense to RV) coupling interval at step 435, method 300 inquires, atdecision step 436, if an intrinsic right ventricular depolarization(R-wave) is detected. If it is, method 300 inhibits the delivery of aright ventricular stimulation pulse at step 438. If an intrinsic rightventricular depolarization is not detection at step 436, themicrocontroller 60 triggers right ventricular output circuitry of theventricular pulse generator 72 to deliver a stimulation pulse to theright ventricle at step 437.

In a similar manner, upon expiration of the left atrial to leftventricular (LAsense to LV) coupling interval at step 445, method 300inquires, at decision step 446, if an intrinsic left ventriculardepolarization (R-wave) is detected. If it is, method 300 inhibits thedelivery of a left ventricular stimulation pulse at step 348. If anintrinsic left ventricular depolarization is not detection at step 446,the microprocessor 60 triggers the left ventricular output circuit ofthe ventricular pulse generator 72 to deliver a stimulation pulse to theleft ventricle at step 447.

Returning now to FIGS. 5 and 6, if the P-wave detection has been made inthe right atrium, the microprocessor 60 commands the timing controlcircuitry 79 to simultaneously initiate three different timers at step220. As it is illustrated in FIG. 9, one timer starts the right atrialsense to left atrium (RAsense to LA) coupling interval (step 455).Another timer simultaneously starts the right atrial sense to rightventricle (RAsense to RV) coupling interval (step 465). The third timerstarts the right atrial sense to left ventricle (RAsense to LV) couplinginterval (step 475). These coupling intervals triggered by a rightatrial sense event may be different than the coupling intervalstriggered by a right atrial pace event as described above in conjunctionwith steps 425, 435, and 445. Upon expiration of the coupling intervals,the stimulation device 10 delivers the required stimulation pulses atstep 322.

FIG. 9 illustrates further details of step 322. Upon expiration of theright atrial sense to left atrium (RAsense to LA) coupling interval atstep 455, method 300 inquires, at decision step 456, if an intrinsicright atrial depolarization (P-wave) is detected. If it is, method 300inhibits the delivery of a left atrial stimulation pulse at step 457. Ifan intrinsic left atrial depolarization is not detection at step 456,the microprocessor 60 triggers the left atrial output circuitry of theatrial pulse generator 70 to deliver a left atrial (LA) stimulationpulse at step 457.

Similarly, upon expiration of the right atrial pace to right ventricular(RApace to RV) coupling interval at step 465, method 300 inquires, atdecision step 466, if an intrinsic right ventricular depolarization(R-wave) is detected. If it is, method 300 inhibits the delivery of aright ventricular stimulation pulse at step 468. If an intrinsic rightventricular depolarization is not detection at step 436, themicrocontroller 60 triggers the ventricular pulse generator 72 todeliver a right ventricular (RV) stimulation pulse at step 467.

In a similar manner, upon expiration of the right atrial sense to leftventricular (RAsense to LV) coupling interval at step 475, method 300inquires, at decision step 476, if an intrinsic left ventriculardepolarization (R-wave) is detected. If it is, method 300 inhibits thedelivery of a left ventricular stimulation pulse at step 478. If anintrinsic left ventricular depolarization is not detection at step 476,the microprocessor 60 triggers the left atrial output circuitry of theventricular pulse generator 72 to deliver a left ventricular (LV)stimulation pulse. After the expiration of these three couplingintervals and the delivery of triggered stimulation to the designatedstimulation sites, method 300 returns to step 202 (FIG. 6) where themicroprocessor 60 initiates a new escape interval to start the nextcardiac cycle.

In this way, the sequential delivery of stimulation pulses to all fourchambers of the heart is precisely controlled in order to providecoordinated depolarization of the cardiac chambers. In this example, thestimulation device 10 essentially operates in a demand pacing mode inthe right and left atria and in a triggered pacing mode in the right andleft ventricles, though other possibilities are similarly feasible, asdescribed herein. Sensing within all of these chambers is stillprovided, however, in order to accommodate the tachycardia detectionfeatures of the stimulation device 10, and to utilize its ability todeliver shocking therapy in addition to pacing therapy as needed.

The programmed settings of the coupling intervals described inconjunction with FIG. 5 are preferably selected in a way that providesoptimal hemodynamic benefit to the patient. A medical practitioner maymanually program these settings based on clinical measurements ofcardiac performance. It is recognized that the selection and programmingof numerous coupling intervals associated with numerous stimulationsites could become a time-consuming task. Therefore, the selection ofcoupling intervals may be semi-automatic or completely automatic. Forexample, after manual programming of the most critical couplingintervals, the microprocessor 60 might calculate other couplingintervals based on mathematical relationships or patient's historystored in memory 90, or apply default values to other couplingintervals.

In an alternative embodiment of the present invention, the optimalcoupling intervals may be selected automatically based on measurementsof cardiac function or other physiological parameters that relate to theclinical condition of the patient as measured by physiological sensor108 and/or impedance measuring circuit 112.

FIG. 10 illustrates a method 500 for automatically adjusting thecoupling intervals. The method 500 may be performed upon delivery of anexternal command, or on a programmed periodic basis, for example, daily.Method 500 starts at step 505 by verifying that the patient is at rest.Preferably, physiological measurements made for comparing cardiac stateduring different pacing modalities is performed only at rest in order toavoid confounding variables that may occur if the patient is engaged invarying levels of activity during the test. Various methods may be usedto verify resting state, such as heart rate or other physiologicalsensor 108 measured parameters. For details regarding one method forverifying resting state reference is made to U.S. Pat. No. 5,476,483 toBornzin.

At step 510, the microprocessor 60 determines the present pacing stateof the stimulation device 10. If the device 10 is programmed to beoperating in a demand mode in both the atrial and ventricular chambers,it may be in one of four pacing states: atrial pacing and ventricularpacing (AV pacing state), atrial pacing and ventricular sensing (ARpacing state), atrial sensing and ventricular pacing (PV pacing state)or atrial sensing and ventricular sensing (PR pacing state).

If the stimulation device 10 is pacing in the ventricle, that is ineither the AV or PV pacing states, an attempt is made to inhibitventricular pacing by extending the atrial-ventricular (AV) delay toallow more time for an intrinsic R-wave to occur at step 515. If thestimulation device 10 is pacing in the atrium, that is in either the AVor AR pacing states, an attempt is made to inhibit atrial pacing byreducing the base pacing rate in order to allow the natural heart rateto predominate at step 520.

Preferably, all pacing is inhibited in order to obtain a baselinephysiologic measurement during the natural resting state of the heart.If ventricular pacing cannot be inhibited, even at the maximum AV delaysetting, such as in the situation of total AV block, no further attemptis made to inhibit ventricular pacing. Atrial pacing may also not beinhibited even at a minimum pacing rate due to sinus node dysfunctionwith either too slow a native sinus rate or an unstable native sinusrate. In such cases, the minimum base pacing rate and a nominal AV delayare applied.

At step 525, a measurement is made using the physiological sensor 108and/or impedance measurement circuit 112 to establish a baseline cardiacfunction. At step 530, the coupling intervals are modulated in a waythat allows testing of numerous combinations of coupling intervals, thusaltering the activation sequence, in order to determine the activationsequence and timing that allows optimal improvement in cardiac state.Initially, coupling intervals between the atria and coupling intervalsbetween the ventricles may be modulated. Next, the AV delay, hereinreferred to as the atrial to ventricular coupling intervals, may bemodulated. Pacing should be sustained for any given set of “test”coupling intervals for a defined minimum time period, such as oneminute, to allow the functional state of the heart to stabilize underthe “test” conditions before making physiological measurements at step535.

Preferably, the stimulation device 10 operates in a trigger modethroughout this test in order to provide a steady cardiac rhythm at eachset of coupling intervals. The physiological measurement made by thesensor 108 and/or the impedance measurement made by impedance measuringcircuit 112 are stored in memory 94 (FIG. 2) with codes indicating thecorresponding coupling interval settings at step 540.

The coupling interval settings resulting in the greatest improvement incardiac function based on sensor 108 measurements and/or impedancecircuit 112 measurements are selected as the final settings. At step545, the optimal coupling interval settings are automaticallyre-programmed. The physiologic sensor 108 measurement and/or theimpedance measuring circuit 112 measurement at these final settingsshould be stored in histogram memory 94 to be recalled and displayedgraphically over time during patient follow-up visits.

Thus, a multichamber or multisite cardiac stimulation device has beenprovided which allows independent sensing and stimulation at multiplesites within the heart according to programmed electrode configurations.Furthermore, a method by which the activation sequence of thestimulated-sites may be precisely controlled using programmable couplingintervals has been provided. Thus, greater flexibility in sensing andstimulation during multisite or multichamber stimulation therapies maybe achieved whereby pacing therapies may be individually tailored topatient need so that optimal hemodynamic or electrophysiological resultsmay be realized.

While detailed descriptions of specific embodiments of the presentinvention have been provided, it would be apparent to those reasonablyskilled in the art that numerous variations of multi-site ormulti-chamber stimulation configurations are possible in which theconcepts and methods of the present invention may readily be applied.The descriptions provided herein, therefore, are for the sake ofillustration and are no way intended to be limiting.

What is claimed is:
 1. A method of automatically controlling anactivation sequence of a plurality of electrodes that are positioned inmultiple cardiac chambers, for use with a multi-site cardiac stimulationdevice, the method comprising the steps of: defining a plurality ofelectrode configurations corresponding to available activation sequencesof the electrodes; selectively delivering a stimulus, on demand, to acardiac chamber; sensing a cardiac event in the cardiac chamber by usinga first electrode configuration; initiating a coupling interval for themultiple cardiac chambers; controlling the activation sequence of theelectrodes by selecting an electrode configuration based on the cardiacchamber in which the cardiac event is sensed or a stimulus delivered;automatically acquiring a measurement of the cardiac event using theelectrode configuration; and automatically adjusting the couplinginterval in response to the measurement of the cardiac event.
 2. Themethod according to claim 1, wherein the sensing step includes sensingintrinsic depolarizations in at least two cardiac chambers.
 3. Themethod according to claim 2, wherein the step of delivering a stimulusincludes stimulating at least two cardiac chambers.
 4. The methodaccording to claim 3, further including the step of determining aninter-atrial conduction (A-A) delay by selecting a coupling intervaldefined according to whether an intrinsic atrial depolarization is firstsensed in a right atrium or in a left atrium.
 5. The method according toclaim 4, wherein the step of automatically adjusting includes selectinga right-to-left atrial coupling interval to control an interval betweenan intrinsic right atrial depolarization (P-wave) and a delivery of aleft atrial stimulus.
 6. The method according to claim 4, wherein thestep of automatically adjusting includes selecting a left-to-rightatrial coupling interval to control an interval between an intrinsicleft atrial depolarization (P-wave) and a delivery of a right atrialstimulus.
 7. The method according to claim 1, wherein the step ofautomatically adjusting further includes adjusting the coupling intervalbased on a stimulation event in any one of the multiple cardiacchambers.
 8. The method according to claim 1, wherein the step ofinitiating a coupling interval includes initiating a unique couplinginterval for a stimulation site, between the stimulation site andremaining stimulation sites, in terms of any one or more of: astimulations event or an intrinsic depolarization occurring at thestimulation site.
 9. The method according to claim 1, further includingsensing an occurrence of an intrinsic atrial depolarization in any oneor more of a left atrium or a right atrium.
 10. The method according toclaim 9, further including delivering a right atrial stimulation pulsewhen no intrinsic atrial depolarization is sensed.
 11. The methodaccording to claim 10, wherein the step of initiating the couplinginterval includes initiating one or more coupling intervals from theright atrial stimulation pulse to any one or more of: a left atrialstimulation pulse, a right ventricular stimulation pulse, or a leftventricular stimulation pulse.
 12. The method according to claim 10,further including detecting an occurrence of an intrinsic right atrialdepolarization.
 13. The method according to claim 12, wherein when theintrinsic right atrial depolarization is not sensed, initiating one ormore coupling intervals from the intrinsic right atrial depolarizationto any one or more of: a left atrial stimulation pulse, a rightventricular stimulation pulse, or a left ventricular stimulation pulse.14. The method according to claim 13, wherein when an intrinsic leftatrial depolarization is sensed, initiating one or more couplingintervals from the intrinsic left atrial depolarization to any one ormore of: a right atrial stimulation pulse, a right ventricularstimulation pulse, or a left ventricular stimulation pulse.
 15. Themethod according to claim 1, further including automatically selecting asensing polarity for each sensing site in the multiple cardiac chambers.16. The method according to claim 15, wherein the step of automaticallyselecting the sensing polarity includes designating any of an anode or acathode assignment to at least one of the plurality of sensingelectrodes.
 17. The method according to claim 16, wherein the step ofdesignating includes selecting a left ventricular tip electrode as thecathode, and further selecting a right ventricular tip electrode as theanode.
 18. The method according to claim 16, wherein the step ofdesignating includes selecting a right ventricular tip electrode as thecathode, and further selecting a left ventricular tip electrode as theanode.
 19. The method according to claim 16, wherein the step ofdesignating includes assigning any of an anodal sensing or a cathodalsensing to at least one of the plurality of sensing electrodes.
 20. Themethod according to claim 16, wherein the step of designating includesassigning any of an anodal sensing or a cathodal sensing to at least oneof the plurality of sensing electrodes.
 21. The method according toclaim 16, further including automatically selecting a stimulationpolarity for each stimulation site in the multiple cardiac chambers. 22.The method according to claim 21, wherein the step of automaticallyselecting the stimulation polarity includes designating any of an anodeor a cathode assignment to at least one of a plurality of stimulationelectrodes.
 23. The method according to claim 22, wherein the step ofdesignating includes selecting a left ventricular tip electrode as thecathode, and further selecting a right ventricular tip electrode as theanode.
 24. The method according to claim 22, wherein the step ofdesignating includes selecting a right ventricular tip electrode as thecathode, and further selecting a left ventricular tip electrode as theanode.
 25. The method according to claim 22, wherein the step ofdesignating includes assigning any of an anodal sensing or a cathodalsensing to at least one of the plurality of sensing electrodes.
 26. Themethod according to claim 1, further including allowing intrinsicdepolarizations occurring at each stimulation site to be sensedindependently.
 27. The method according to claim 1, wherein the step ofautomatically adjusting the coupling interval includes determining acurrent stimulation state of the stimulation device; when thestimulation device is stimulating a ventricle, attempting to inhibitventricular stimulation by extending an atrial-ventricular (AV) delay;when the stimulation device is stimulating an atrium, attempting toinhibit atrial pacing by reducing a base pacing rate; measuring one ormore baseline physiological parameters; and modulating one or morecombinations of the coupling intervals for altering the activationsequence so as to determine an activation sequence that allows optimalimprovement in the current stimulation state.
 28. A multi-site cardiacstimulation device capable of automatically controlling an activationsequence of a plurality of electrodes that are positioned in multiplecardiac chambers, comprising: a discriminator, coupled to the pluralityof electrodes, that senses a cardiac signal in each of the cardiacchambers, and that identifies a cardiac chamber of origin in which thecardiac signal originates; a pulse generator, connected to theelectrodes, to selectively deliver stimulation pulses on demand to thecardiac chambers; and timing control circuitry, connected to theelectrodes, the pulse generator, and the discriminator to initiatecoupling intervals for the multiple cardiac chambers based on thecardiac chamber of origin in which an intrinsic depolarization is sensedor a stimulus is delivered, for controlling a timing of the activationsequence, and the timing control circuitry further automaticallyadjusting the coupling intervals based on measurements acquired by thediscriminator.
 29. The stimulation device according to claim 28, whereinthe discriminator senses an occurrence of an intrinsic atrialdepolarization in any one or more of a left atrium or a right atrium.30. The stimulation device according to claim 29, wherein the pulsegenerator delivers a right atrial stimulation pulse in the absence of anintrinsic atrial depolarization.
 31. The stimulation device according toclaim 30, wherein the plurality of electrodes include stimulationelectrodes; and further including a switch bank that automaticallyselects polarities for the plurality of stimulation electrodes.
 32. Thestimulation device according to claim 30, further including a multi-portconnector for connection to any one or more of uni-polar, bi-polar, ormulti-polar leads.
 33. The stimulation device according to claim 32,wherein the multi-port connector includes four bipolar connection ports:a left ventricular connection port that couples to a left ventricularlead with terminals associated with a ventricular tip electrode, a leftventricular ring electrode, and a left atrial coil electrode; a leftatrial connection port that couples to a left atrial lead with terminalsassociated with a left atrial tip electrode and a left atrial ringelectrode; a right ventricular connection port that couples to a rightventricular lead with terminals associated with a right ventricular tipelectrode, a right ventricular ring electrode, a right ventricularshocking coil, and a right ventricular coil electrode; and a rightatrial connection port that couples to a right atrial lead withterminals associated with a right atrial tip electrode and a rightatrial ring electrode.
 34. The stimulation device according to claim 29,wherein the timing control circuitry initiates one or more couplingintervals from a right atrial stimulation pulse to any one or more of: aleft atrial stimulation pulse, a right ventricular stimulation pulse, ora left ventricular stimulation pulse.
 35. The stimulation deviceaccording to claim 29, wherein the sensing circuitry is adapted tofurther sense an occurrence of an intrinsic right atrial depolarization;and wherein in the absence of an intrinsic right atrial depolarization,the timing control circuitry initiates one or more coupling intervalsfrom the intrinsic right atrial depolarization to any one or more of: aleft atrial stimulation pulse, a right ventricular stimulation pulse, ora left ventricular stimulation pulse.
 36. The stimulation deviceaccording to claim 29, wherein in the presence of an intrinsic leftatrial depolarization, the sensing circuitry initiates one or morecoupling intervals from the intrinsic left atrial depolarization to anyone or more of: a right atrial stimulation pulse, a right ventricularstimulation pulse, or a left ventricular stimulation pulse.
 37. Thestimulation device according to claim 28, wherein the plurality ofelectrodes include sensing electrodes; and further including a switchbank that automatically selects polarities for the plurality of sensingelectrodes.
 38. A multi-site cardiac stimulation device capable ofautomatically controlling an activation sequence of a plurality ofelectrodes that are positioned in multiple cardiac chambers, comprising:means for sensing a cardiac signal in each of the multiple cardiacchambers; means for detecting a cardiac chamber of origin in which thecardiac signal originates; means for selectively generating stimulationenergy, on demand, to the multiple cardiac chambers; and means forinitiating coupling intervals for the multiple cardiac chambers based onthe cardiac chamber of origin in which an intrinsic depolarization issensed or a stimulus is delivered, for controlling a timing of theactivation sequence, and for automatically adjusting the couplingintervals based on measurements acquired by the sensing means.
 39. Thestimulation device according to claim 38, wherein the sensing meanssenses an occurrence of an intrinsic atrial depolarization in any one ormore of a left atrium or a right atrium.
 40. The stimulation deviceaccording to claim 39, wherein the means for generating stimulationenergy delivers a right atrial stimulation pulse in the absence of anintrinsic atrial depolarization; wherein the initiating means initiatesone or more coupling intervals from a right atrial stimulation pulse toany one or more of: a left atrial stimulation pulse, a right ventricularstimulation pulse, or a left ventricular stimulation pulse; wherein inthe absence of an intrinsic right atrial depolarization, the initiatingmeans initiates one or more coupling intervals from the intrinsic rightatrial depolarization to any one or more of: a left atrial stimulationpulse, a right ventricular stimulation pulse, or a left ventricularstimulation pulse; and wherein in the presence of an intrinsic leftatrial depolarization, the initiating means initiates one or morecoupling intervals from the intrinsic left atrial depolarization to anyone or more of: a right atrial stimulation pulse, a right ventricularstimulation pulse, or a left ventricular stimulation pulse.
 41. Thestimulation device according to claim 38, wherein the plurality ofelectrodes include sensing electrodes; and further including switchingmeans for automatically selecting polarities for the plurality ofsensing electrodes.
 42. The stimulation device according to claim 38,wherein the plurality of electrodes include stimulation electrodes; andfurther including switching means for automatically selecting polaritiesfor the plurality of stimulation electrodes.
 43. The stimulation deviceaccording to claim 38, further including a multi-port connecting meansfor connection to any one or more of uni-polar, bi-polar, or multi-polarleads; and wherein the multi-port connecting means includes four bipolarconnection ports: a left ventricular connection port that couples to aleft ventricular lead with terminals associated with a ventricular tipelectrode, a left ventricular ring electrode, and a left atrial coilelectrode; a left atrial connection port that couples to a left atriallead with terminals associated with a left atrial tip electrode and aleft atrial ring electrode; a right ventricular connection port thatcouples to a right ventricular lead with terminals associated with aright ventricular tip electrode, a right ventricular ring electrode, aright ventricular shocking coil, and a right ventricular coil electrode;and a right atrial connection port that couples to a right atrial leadwith terminals associated with a right atrial tip electrode and a rightatrial ring electrode.